The present invention relates to an improved chromatographic separation process for purifying the polyunsaturated fatty acid EPA or a derivative thereof.
EPA and its derivatives are precursors for biologically important molecules, which play an important role in the regulation of biological functions such as platelet aggregation, inflammation and immunological responses. Thus, EPA and its derivatives may be therapeutically useful in treating a wide range of pathological conditions including CNS conditions; neuropathies, including diabetic neuropathy; cardiovascular diseases; general immune system and inflammatory conditions, including inflammatory skin diseases.
EPA is found in natural raw materials, and in particular fish oils. The EPA in fish oils is, however, present in such oils in admixture with saturated fatty acids and numerous other impurities.
Purification of EPA from fish oils is particularly challenging. Thus, fish oils are extremely complex mixtures containing a large number of different components with very similar retention times in chromatography apparatuses. They represent a much more challenging feedstock from which to purify EPA than, for example, an algal oil feedstock. However, a very high degree of purity of EPA is required, particularly for pharmaceutical and nutraceutical applications. Historically, therefore, distillation has been used to purify EPA for therapeutic applications.
Unfortunately, EPA is extremely fragile. Thus, when heated in the presence of oxygen, it is prone to isomerization, peroxidation and oligomerization. The fractionation and purification of EPA to prepare pure fatty acids is therefore difficult. Distillation, even under vacuum, can lead to non-acceptable product degradation.
Simulated and actual moving bed chromatography are known techniques, familiar to those of skill in the art. The principle of operation involves countercurrent movement of a liquid eluent phase and a solid adsorbent phase. This operation allows minimal usage of solvent making the process economically viable. Such separation technology has found several applications in diverse areas, including hydrocarbons, industrial chemicals, oils, sugars and APIs.
As is well known, in a conventional stationary bed chromatographic system, a mixture whose components are to be separated percolates through a container. The container is generally cylindrical, and is typically referred to as the column. The column contains a packing of a porous material (generally called the stationary phase) exhibiting a high permeability to fluids. The percolation velocity of each component of the mixture depends on the physical properties of that component so that the components exit from the column successively and selectively. Thus, some of the components tend to fix strongly to the stationary phase and thus will percolate slowly, whereas others tend to fix weakly and exit from the column more quickly. Many different stationary bed chromatographic systems have been proposed and are used for both analytical and industrial production purposes.
In contrast, a simulated moving bed chromatography apparatus consists of a number of individual columns containing adsorbent which are connected together in series. Eluent is passed through the columns in a first direction. The injection points of the feedstock and the eluent, and the separated component collection points in the system, are periodically shifted by means of a series of valves. The overall effect is to simulate the operation of a single column containing a moving bed of the solid adsorbent, the solid adsorbent moving in a countercurrent direction to the flow of eluent. Thus, a simulated moving bed system consists of columns which, as in a conventional stationary bed system, contain stationary beds of solid adsorbent through which eluent is passed, but in a simulated moving bed system the operation is such as to simulate a continuous countercurrent moving bed.
Processes and equipment for simulated moving bed chromatography are described in several patents, including U.S. Pat. No. 2,985,589, U.S. Pat. No. 3,696,107, U.S. Pat. No. 3,706,812, U.S. Pat. No. 3,761,533, FR-A-2103302, FR-A-2651148 and FR-A-2651149, the entirety of which are incorporated herein by reference. The topic is also dealt with at length in “Preparative and Production Scale Chromatography”, edited by Ganetsos and Barker, Marcel Dekker Inc, New York, 1993, the entirety of which is incorporated herein by reference.
An actual moving bed system is similar in operation to a simulated moving bed system. However, rather than shifting the injection points of the feed mixture and the eluent, and the separated component collection points by means of a system of valves, instead a series of adsorption units (i.e. columns) are physically moved relative to the feed and drawoff points. Again, operation is such as to simulate a continuous countercurrent moving bed.
Processes and equipment for actual moving bed chromatography are described in several patents, including U.S. Pat. No. 6,979,402, U.S. Pat. No. 5,069,883 and U.S. Pat. No. 4,764,276, the entirety of which are incorporated herein by reference.
A typical simulated moving bed chromatography apparatus is illustrated with reference to FIG. 1. The concept of a simulated or actual moving bed chromatographic separation process is explained by considering a vertical chromatographic column containing stationary phase S divided into sections, more precisely into four superimposed sub-zones I, II, III and IV going from the bottom to the top of the column. The eluent is introduced at the bottom at IE by means of a pump P. The mixture of the components A and B which are to be separated is introduced at IA+B between sub-zone II and sub-zone III. An extract containing mainly B is collected at SB between sub-zone I and sub-zone II, and a raffinate containing mainly A is collected at SA between sub-zone III and sub-zone IV.
In the case of a simulated moving bed system, a simulated downward movement of the stationary phase S is caused by movement of the introduction and collection points relative to the solid phase. In the case of an actual moving bed system, simulated downward movement of the stationary phase S is caused by movement of the various chromatographic columns relative to the introduction and collection points. In FIG. 1, eluent flows upward and mixture A+B is injected between sub-zone II and sub-zone III. The components will move according to their chromatographic interactions with the stationary phase, for example adsorption on a porous medium. The component B that exhibits stronger affinity to the stationary phase (the slower running component) will be more slowly entrained by the eluent and will follow it with delay. The component A that exhibits the weaker affinity to the stationary phase (the faster running component) will be easily entrained by the eluent. If the right set of parameters, especially the flow rate in each sub-zone, are correctly estimated and controlled, the component A exhibiting the weaker affinity to the stationary phase will be collected between sub-zone III and sub-zone IV as a raffinate and the component B exhibiting the stronger affinity to the stationary phase will be collected between sub-zone I and sub-zone II as an extract.
To achieve high purity EPA or EPA ethyl ester in purities of greater than 90%, for example greater than 95 or 97%, it is possible to utilise a simulated moving bed separation process which performs two simultaneous separation steps. Such a process is described in international patent application no. PCT/GB10/002339, the entirety of which is incorporated herein by reference.
In general, all chromatographic separation techniques for separating PUFAs, including SMB processes, utilise large volumes of organic solvents as eluents. After the chromatographic separation process is completed the PUFAs must be recovered from solution in the eluent. Typically a large expenditure of time and energy is involved in recovering PUFAs from solution in the eluent. Furthermore, organic solvents used as eluents in chromatographic separation processes are frequently harmful to the environment or to the operatives handling them. Therefore, a chromatographic separation process which reduces the amount of organic solvent that needs to be used is required.
It has now been advantageously found that EPA or an EPA derivative can be produced in a similarly high purity as described in PCT/GB10/002339 by a three-step separation process which uses a much lower volume of solvent that the two-step process. The improved process of the present invention utilises almost 50% less solvent than the two-step process described in PCT/GB10/002339. This is clearly advantageous in terms of cost, ease of recovery of product, and environmental impact.